Non-blocking, full-mesh data center network having optical permutors

ABSTRACT

A network system for a data center is described in which a switch fabric provides full mesh interconnectivity such that any servers may communicate packet data to any other of the servers using any of a number of parallel data paths. Moreover, according to the techniques described herein, edge-positioned access nodes, optical permutation devices and core switches of the switch fabric may be configured and arranged in a way such that the parallel data paths provide single L2/L3 hop, full mesh interconnections between any pairwise combination of the access nodes, even in massive data centers having tens of thousands of servers. The plurality of optical permutation devices permute communications across the optical ports based on wavelength so as to provide full-mesh optical connectivity between edge-facing ports and core-facing ports without optical interference.

This application claims the benefit of U.S. Provisional Appl. No.62/478,414, filed Mar. 29, 2017, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The invention relates to computer networks and, more particularly, datacenter network interconnects.

BACKGROUND

In a typical cloud-based data center, a large collection ofinterconnected servers provides computing and/or storage capacity forexecution of various applications. For example, a data center maycomprise a facility that hosts applications and services forsubscribers, i.e., customers of the data center. The data center may,for example, host all of the infrastructure equipment, such as computenodes, networking and storage systems, redundant power supplies, andenvironmental controls.

In most data centers, clusters of storage systems and applicationservers are interconnected via high-speed switch fabric provided by oneor more tiers of physical network switches and routers. Moresophisticated data centers provide infrastructure spread throughout theworld with subscriber support equipment located in various physicalhosting facilities.

SUMMARY

In general, this disclosure describes data center network systems.Example implementations of network systems for data centers aredescribed in which a switch fabric provides full mesh interconnectivitysuch that any of the servers may communicate packet data to any other ofthe servers using any of a number of parallel data paths. In exampleimplementations, the full mesh interconnectivity may be non-blocking anddrop-free.

Moreover, according to the techniques described herein, access nodescoupled to the servers, intermediate optical permutation devices, andcore switches of the switch fabric may be configured and arranged in away such that the parallel data paths in the switch fabric providesingle L2/L3 hop, full mesh interconnections between any pairwisecombination of the access nodes, even in massive data centers havingtens of thousands of servers. A plurality of optical permutation devicesoptically couple the access nodes to the core switches by optical linksto communicate the data packets between the access nodes and the coreswitches as optical signals. Each of the optical permutation devicescomprises a set of input optical ports and a set of output optical portsto direct optical signals between the access nodes and the core switchesto communicate the data packets. Each of the optical permutation devicesis configured such that optical communications received from inputoptical ports are permuted across the output optical ports based onwavelength so as to provide full-mesh optical connectivity between theedge-facing ports and the core-facing ports without opticalinterference.

In some example implementations, this disclosure is directed to anoptical permutor that operates as an optical interconnect fortransporting optical communications between network devices, such asdevices within a data center. As described herein, the optical permutorprovides a plurality of input ports that receive respective opticalinput signals, each potentially carrying optical communications at aplurality of different wavelengths. Internal optical elements of theoptical permutor are configured such that optical communicationsreceived from input ports are “permutated” across output optical portsbased on wavelength so as to provide full-mesh connectivity between theports and in a manner that guarantees no optical interference due towavelength collision. That is, the optical permutor is configured toensure that optical communications received from any one of the opticalinput ports can be directed to any one of the optical output portswithout optical interference with any simultaneous communications on anyof the other input ports. Moreover, the optical permutor may bebi-directional. In this way, the optical permutors may providebi-directional, full-mesh point-to-point connectivity for transportingoptical communications.

In one example, a network system comprises a plurality of servers, aswitch fabric comprising a plurality of core switches, a plurality ofaccess nodes, each of the access nodes coupled to a subset of theservers to communicate data packets with the servers, and a plurality ofoptical permutation devices optically coupling the access nodes to thecore switches by optical links to communicate the data packets betweenthe access nodes and the core switches as optical signals. Each theoptical permutation devices comprises a set of input optical ports and aset of output optical ports to direct optical signal between the accessnodes and the core switches to communicate the data packets. Moreover,each of the optical permutation devices is configured such that opticalcommunications received from the input optical ports are permuted acrossthe output optical ports based on wavelength so as to provide full-meshoptical connectivity between the input optical ports and the outputoptical ports without optical interference.

In another example, a method comprises interconnecting a plurality ofservers of a data center by an intermediate network comprising: a switchfabric comprising a plurality of core switches; a plurality of accessnodes, each of the access nodes coupled to a subset of the servers tocommunicate data packets with the servers; and a plurality of opticalpermutation devices optically coupling the access nodes to the coreswitches by optical links to communicate the data packets between theaccess nodes and the core switches as optical signals. Each of theoptical permutation device comprise a set of input optical ports and aset of output optical ports to direct optical signal between the accessnodes and the core switches to communicate the data packets, and each ofthe optical permutation devices is configured such that opticalcommunications received from the input optical ports are permuted acrossthe output optical ports based on wavelength to provide full-meshoptical connectivity between the input optical ports and the outputoptical ports without optical interference. Moreover, the access nodes,the core switches, and the optical permutation devices are configured toprovide a plurality of parallel data paths between each pairwisecombination of the access nodes. The method further comprisescommunicating a packet flow between the servers including spraying, withthe access nodes, packets of the packet flow across the plurality ofparallel data paths between the access nodes, and reordering, with theaccess nodes, the packets into the packet flow and delivering thereordered packets.

In another example, a method comprises receiving packet communicationswith a set of optical input ports of an optical permutation device,wherein the set of optical input ports couple the optical permutationdevice to a set of access nodes positioned between the opticalpermutation device and a set of servers with a packet-based network. Themethod further comprises permuting the packet-based communicationsacross a set of output optical ports of the optical permutor based onwavelength to provide full-mesh optical connectivity between the inputoptical ports and the output optical ports of the optical permutorwithout optical interference, and forwarding, with the optical permutorand by the set of output ports, the permuted packet-based communicationstoward a set of one or more switches within the networks.

In another example, an optical permutation device comprises a pluralityof the input optical ports to receive respective optical signals,wherein the respective optical signals comprise optical communicationsat a plurality of different wavelengths. The optical permutation devicefurther comprises a plurality of the output optical ports to outputoptical signals; and a set of optical elements arranged to provideoptical interconnection between the optical input ports and the opticaloutput ports. The set of optical elements are configured to direct arespective unique and non-interfering permutation of the wavelengthsfrom the input optical ports to the output optical ports.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the invention will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example network having a datacenter in which examples of the techniques described herein may beimplemented.

FIG. 2A is a block diagram illustrating an example optical permutor inaccordance with the techniques described herein.

FIG. 2B is a block diagram showing, in further detail, an exampleimplementation of example multiplexor slices of the example opticalpermutor of FIG. 2A.

FIG. 3A is a block diagram showing another example implementation of anoptical permutor in accordance with the techniques described herein.

FIG. 3B is a block diagram showing an example implementation of opticaldemultiplexors for the optical permutor of FIG. 3A.

FIG. 4 is a block diagram illustrating an optical permutor having aplurality of logical planes, each of the planes arranged to operate asan optical permutor as described herein.

FIG. 5 is a block diagram illustrating a more detailed exampleimplementation of a network in which a set of optical permutationdevices is utilized to interconnect endpoints.

Like reference characters denote like elements throughout the figuresand text.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an example network 8 having adata center 10 in which examples of the techniques described herein maybe implemented. In general, data center 10 provides an operatingenvironment for applications and services for customers 11 coupled tothe data center by content/service provider network 7. In otherexamples, content/service provider network 7 may be a data center widearea network (DC WAN), private network or other type of network. Datacenter 10 may, for example, host infrastructure equipment, such ascompute nodes, networking and storage systems, redundant power supplies,and environmental controls. Content/service provider network 7 may becoupled to one or more networks administered by other providers, and maythus form part of a large-scale public network infrastructure, e.g., theInternet.

In some examples, data center 10 may represent one of manygeographically distributed network data centers. In the example of FIG.1, data center 10 is a facility that provides network services forcustomers 11. Customers 11 may be collective entities such asenterprises and governments or individuals. For example, a network datacenter may host web services for several enterprises and end users.Other exemplary services may include data storage, virtual privatenetworks, traffic engineering, file service, data mining, scientific- orsuper-computing, and so on.

In this example, data center 10 includes a set of storage systems andapplication servers 12 interconnected via high-speed switch fabric 14.In some examples, servers 12 are arranged into multiple different servergroups, each including any number of servers up to, for example, nservers 12 ₁-12 _(n). Servers 12 provide execution and storageenvironments for applications and data associated with customers 11 andmay be physical servers, virtual machines, virtualized containers orcombinations thereof.

In the example of FIG. 1, each of servers 12 is coupled to switch fabric14 by an access node 17. As further described herein, in one example,each access node 17 is a highly programmable I/O processor speciallydesigned for offloading certain stream processing functions, such asfrom servers 12. In one example, each of access nodes 17 includes one ormore processing cores consisting of a number of internal processorclusters, e.g., MIPS cores, equipped with hardware engines that offloadcryptographic functions, compression and regular expression (RegEx)processing, data storage functions and networking operations. In thisway, each access node 17 includes components for fully implementing andprocessing network and storage stacks on behalf of one or more servers12. In addition, access nodes 18 may be programmatically configured toserve as a security gateway for its respective servers 12, freeing upthe processors of the servers to dedicate resources to applicationworkloads. In some example implementations, each access node 17 may beviewed as a network interface subsystem that implements full offload ofthe handling of data packets (with zero copy in server memory) andstorage acceleration for the attached server systems. In one example,each access node 17 may be implemented as one or moreapplication-specific integrated circuit (ASIC) or other hardware andsoftware components, each supporting a subset of the servers. Accessnodes 17 may also be referred to as data processing units (DPUs), ordevices including DPUs. In other words, the term access node may be usedherein interchangeably with the term DPU. Additional example details ofvarious example access nodes are described in U.S. Provisional PatentApplication No. 62/559,021, filed Sep. 15, 2017, entitled “Access Nodefor Data Centers,” and U.S. Provisional Patent Application No.62/530,691, filed Jul. 10, 2017, entitled “Data Processing Unit forComputing Devices,” the entire contents of both being incorporatedherein by reference.

In some examples, access nodes 17 may be arranged into multipledifferent access node groups 19, each including any number of accessnodes up to, for example, x access nodes 17 ₁-17 _(x). As shown in FIG.1, each access node 17 provides connectivity to switch fabric 14 for adifferent group of servers 12 and may be assigned respective IPaddresses and provide routing operations for the servers 12 coupledthereto. As described herein, access nodes 17 provide routing and/orswitching functions for communications from/directed to the individualservers 12. For example, as shown in FIG. 1, each access node 17includes a set of edge-facing network interfaces for communicatingtoward a respective group of servers 12 and one or more core-facingoptical interfaces for communicating toward core switches 22. In oneexample, core switches 22 comprise a set of interconnected,high-performance yet off-the-shelf silicon-based packet routers andswitches that implement industry standard protocols. In some exampleimplementations, each core switch may maintain the same routing tablethat defines forwarding information for switching packets between portsbased on the destination of the packets. The routing table may bestatically programmed, learned by way of routing protocols, configuredby a network management system, configured by controller 21 or othermeans.

In the example of FIG. 1, each access node 17 provides connectivity toswitch fabric 14 for a different group of servers 12 and may be assignedrespective IP addresses and provide routing operations for the servers12 coupled thereto. As described herein, access nodes 17 provide routingand/or switching functions for communications from/directed to theindividual servers 12. For example, as shown in FIG. 1, each access node17 includes a set of edge-facing electrical or optical local businterfaces for communicating with a respective group of servers 12 andone or more core-facing electrical or optical interfaces forcommunicating with core switches 22 within switch fabric 14. Inaddition, access nodes 17 described herein may provide additionalservices, such as storage (e.g., integration of solid-state storagedevices), security (e.g., encryption), acceleration (e.g., compression),I/O offloading, and the like. In some examples, one or more of accessnodes 17 may include storage devices, such as high-speed solid-statedrives or rotating hard drives, configured to provide network accessiblestorage for use by applications executing on the servers. Although notshown in FIG. 1, access nodes 17 may be directly coupled to each other,such as direct coupling between access nodes in a common access nodegroup 19, to provide direct interconnectivity between the access nodesof the same group. For example, multiple access nodes 17 (e.g., 4 accessnodes) may be positioned within a common access node group 19 forservicing a group of servers (e.g., 16 servers). More details on thedata center network architecture and interconnected access nodes areavailable in U.S. Provisional Patent Application No. 62/514,583, filedJun. 2, 2017, entitled “Non-Blocking Any-to-Any Data Center Network withPacket Spraying Over Multiple Alternate Data Paths,” the entire contentof which is incorporated herein by reference.

As described herein, switch fabric 14 includes a set of opticalpermutors 32 ₁-32 _(Y) (herein, “optical permutors 32”), also referredto as optical permutation devices, connected to a set of corepacket-based switches 22 that collectively provide full meshpoint-to-point connectivity between servers 12. As further explained,optical permutors 32 are optical interconnect devices that transportoptical signals between access nodes 17 and core switches 22 byutilizing wavelength division multiplexing such that communications forservers 12 of the same server group may be conveyed through a commonoptical fiber 37. For example, each access node 17 may utilize differentwavelengths for conveying communications for servers 12 of the sameserver group. In the example of in FIG. 1, each optical permutor 32includes a set of edge-facing optical interfaces 36 ₁-36 _(x) foroptical communication with a respective group of access nodes 17 ₁-17_(x) and a set of core-facing optical interfaces 38 ₁-38 _(x) forcommunicating with core switches 22. Although each optical permutor 32is illustrated in FIG. 1 as including the same number, x, of accessnodes 17 and edge-facing optical interfaces 36, in other examples eachoptical permutor 32 may include optical interfaces 36 that are eachcapable of coupling to more than one optical fiber 37. In this otherexample, each optical permutor 32 may include a set of edge-facingoptical interfaces 36 ₁-36 _(x) for optical communication with aninteger multiple of x, e.g., 2×, 3×, or 4×, of access nodes 17.

Furthermore, as described herein, each optical permutor 32 is configuredsuch that optical communications received from downstream ports 36 are“permuted” across upstream ports 38 based on wavelength so as to providefull-mesh connectivity between the upstream and downstream ports withoutany optical interference. That is, each optical permutor 32 isconfigured to ensure that optical communications received from any oneof downstream servers 12 can be directed to any upstream-facing opticalports 38 without optical interference with any simultaneouscommunications from any other server 12. Moreover, optical permutors 32may be bi-directional, i.e., similarly configured to permutecommunications from upstream ports 38 across downstream ports 36 suchthat no optical interference occurs on any of the downstream ports. Inthis way, optical permutors 32 provide bi-directional, full-meshpoint-to-point connectivity for transporting communications for servers12 to/from core switches 22.

For example, optical permutor 32 ₁ is configured to optically directoptical communications from downstream-facing ports 36 ₁-36 _(x) outupstream-facing ports 38 ₁-38 _(x) such that each upstream port 38carries a different one of the possible unique permutations of thecombinations of downstream-facing ports 36 and the optical frequenciescarried by those ports, where no single upstream-facing port 38 carriescommunications from servers 12 associated with the same wavelength. Assuch, in this example, each upstream-facing port 38 carries anon-interfering wavelength from each of the downstream facing ports 36,thus allowing a full mesh of communication. In FIG. 1, each of thedownstream-facing optical ports 36 of each optical permutor 32 receivesan optical signal carrying, in this example, up to N wavelengths for upto N servers of a server group. As one example, port 36 ₁ of opticalpermutor 32 ₁ may receive an optical signal from access node 17 ₁,carrying communications as N different wavelengths, where eachwavelength is reserved for communications associated with a differentone of servers 12 of the server group coupled to access node 17 ₁.Optical permutor 32 ₁ directs the optical communications fromdownstream-facing ports 36 to upstream-facing ports 38 such that eachupstream-facing port 38 carries a different unique permutation of theoptical frequencies/down-stream port combinations and where noupstream-facing port 38 carries communications from servers 12associated with the same wavelength. Moreover, optical permutor 32 ₁ maysimilarly be configured in a bi-directional manner to permutecommunications from upstream-facing ports 38 ₁-38 _(x) acrossdownstream-facing ports 36 ₁-36 _(x) and so that no downstream-facingport 36 carries communications associated with the same wavelength,thereby providing full bi-directional, full-mesh point-to-pointconnectivity for transporting communications for servers 12 to/from coreswitches 22.

In this way, switch fabric 14 may provide full mesh interconnectivitysuch that any of servers 12 may communicate packet data to any other ofthe servers 12 using any of a number of parallel data paths. Moreover,according to the techniques described herein, switch fabric 14 may beconfigured and arranged in a way such that the parallel data paths inswitch fabric 14 provides single L2/L3 hop, full mesh interconnections(bipartite graph) between servers 12, even in massive data centershaving tens of thousands of servers. In some example implementations,each access node 17 may logically be connected to each core switch 22and, therefore, have multiple parallel data paths for reaching any givenother access node and the servers 12 reachable through those accessnodes. As such, in this example, for M core switches 22, M possible datapaths exist between each access node 17. Each access node 17 may beviewed as effectively connected to each core switch 22 and thus anyaccess node sourcing traffic into switch fabric 14 may reach any otheraccess node 17 by a single, one-hop L3 lookup by an intermediate device(core switch).

Further, in some embodiments, rather than being limited to flow-basedrouting and switching, switch fabric 14 may be configured such thataccess nodes 17 may, for any given packet flow between servers 12, spraythe packets of a packet flow across all or a subset of the parallel datapaths of switch fabric 14 by which a given destination access node 17for a destination server 12 can be reached. An access node 17 sourcing apacket flow for a source server 12 may use any technique for sprayingthe packets across the available parallel data paths, such as random,round-robin, hash-based or other mechanism that may be designed tomaximize, for example, utilization of bandwidth or otherwise avoidcongestion. In some example implementations, flow-based load balancingneed not necessarily be utilized and more effective bandwidthutilization may be used by allowing packets of a given packet flow (fivetuple) sourced by a server 12 to traverse different paths of switchfabric 14 between access nodes 17 coupled to the source and destinationsservers. The respective destination access node 17 associated with thedestination server 12 may be configured to reorder the variable lengthIP packets of the packet flows and deliver the packets to thedestination server in reordered sequence.

In this way, according to the techniques herein, example implementationsare described in which access nodes 17 interface and utilize switchfabric 14 so as to provide full mesh (any-to-any) interconnectivity suchthat any of servers 12 may communicate packet data for a given packetflow to any other of the servers using any of a number of parallel datapaths within the data center 10. For example, example networkarchitectures and techniques are described in which access nodes, inexample implementations, spray individual packets for packet flowsbetween the access nodes and across some or all of the multiple paralleldata paths in the data center switch fabric 14 and reorder the packetsfor delivery to the destinations so as to provide full meshconnectivity.

As described herein, the techniques of this disclosure introduce a newdata transmission protocol referred to as a Fabric Control Protocol(FCP) that may be used by the different operational networkingcomponents of any of access nodes 17 to facilitate communication of dataacross switch fabric 14. As further described, FCP is an end-to-endadmission control protocol in which, in one example, a sender explicitlyrequests a receiver with the intention to transfer a certain number ofbytes of payload data. In response, the receiver issues a grant based onits buffer resources, QoS, and/or a measure of fabric congestion. Ingeneral, FCP enables spray of packets of a flow to all paths between asource and a destination node, and may provide any of the advantages andtechniques described herein, including resilience against request/grantpacket loss, adaptive and low latency fabric implementations, faultrecovery, reduced or minimal protocol overhead cost, support forunsolicited packet transfer, support for FCP capable/incapable nodes tocoexist, flow-aware fair bandwidth distribution, transmit buffermanagement through adaptive request window scaling, receive bufferoccupancy based grant management, improved end to end QoS, securitythrough encryption and end to end authentication and/or improved ECNmarking support. More details on the FCP are available in U.S.Provisional Patent Application No. 62/566,060, filed Sep. 29, 2017,entitled “Fabric Control Protocol for Data Center Networks with PacketSpraying Over Multiple Alternate Data Paths,” the entire content ofwhich is incorporated herein by reference.

Although not shown in FIG. 1, access nodes 17 may be directly coupled,such as access nodes in a common rack, so as to provide directinterconnectivity between the access nodes of the same group. Forexample, multiple access nodes 17 (e.g., 4) may be positioned within acommon server rack holding multiple (e.g., 4) sets of server groups(e.g., 16 servers per server group; 64 servers per rack) along with oneor more optical permutors 32. Each access node 17 of the rack may beinterconnected to the other access nodes of the rack and coupled to theoptical permutors 32 of the rack, which are in turn coupled to one ormore core switches 22 that interconnect multiple server racks. In oneexample, each access node 17 may be implemented as one or moreapplication-specific integrated circuit (ASIC) or other hardware andsoftware components, each supporting a subset of the servers.

In some examples, multiple access nodes 17 may be grouped (e.g., withina single electronic device or appliance), referred to herein as anaccess node group 19, for providing connectivity to a group of serverssupported by the set of access nodes internal to the device. In oneexample, an access node group 19 may comprise four access nodes 17, eachsupporting four servers so as to support a group of sixteen servers. Asone example, each access node 17 may support eight 100 Gigabit Ethernetinterfaces for communicating with other access nodes 17 or an opticalpermutor 32, and a 6×16-lane (i.e., a “96 lane”) PCIe interface forcommunicating with servers 12.

In one example, each access node 17 implements four differentoperational components or functions: (1) a source component operable toreceive traffic from server 12, (2) a source switching componentoperable to switch source traffic to other source switching componentsof different access nodes 17 (possibly of different access node groups)or to core switches 22, (3) a destination switching component operableto switch inbound traffic received from other source switchingcomponents or from cores switches 22 and (4) a destination componentoperable to reorder packet flows and provide the packet flows todestination servers 12.

In this example, servers 12 are connected to source components of theaccess nodes 17 to inject traffic into the switch fabric 14, and servers12 are similarly coupled to the destination component within the accessnodes 17 to receive traffic therefrom. Because of the full-mesh,parallel data paths provided by switch fabric 14, each source switchingcomponent and destination switching component within a given access node17 need not perform L2/L3 switching. Instead, access nodes 17 may applyspraying algorithms to spray packets of a packet flow, e.g., randomly,round-robin, based on QoS/scheduling or otherwise to efficiently forwardpackets without requiring packet analysis and lookup operations.Destination switching components of the ASICs may provide a limitedlookup necessary only to select the proper output port for forwardingpackets to local servers 12. As such, with respect to full routingtables for the data center, only core switches 22 may need to performfull lookup operations. Thus, switch fabric 14 provides ahighly-scalable, flat, high-speed interconnect in which servers 12 areeffectively one L2/L3 hop from any other server 12 within the datacenter.

In the example of FIG. 1, software-defined networking (SDN) controller21 provides a high-level controller for configuring and managing routingand switching infrastructure of data center 10. SDN controller 21provides a logically and in some cases physically centralized controllerfor facilitating operation of one or more virtual networks within datacenter 10 in accordance with one or more embodiments of this disclosure.In some examples, SDN controller 21 may operate in response toconfiguration input received from a network administrator. In someexamples, SDN controller 21 operates to configure access nodes 17 tologically establish one or more virtual fabrics as overlay networksdynamically configured on top of the physical underlay network providedby switch fabric 14, in accordance with the techniques described herein.For example, SDN controller 21 may learn and maintain knowledge ofaccess nodes 21 and establish a communication control channel with eachof the access nodes. SDN controller 21 uses its knowledge of accessnodes 17 to define multiple sets (groups) of two of more access nodes 17to establish different virtual fabrics over switch fabric 14. Morespecifically, SDN controller 21 may use the communication controlchannels to notify each of access nodes 17 for a given set which otheraccess nodes are included in the same set. In response, access nodes 17dynamically setup FCP tunnels with the other access nodes included inthe same set as a virtual fabric over packet switched network 410. Inthis way, SDN controller 21 defines the sets of access nodes 17 for eachof the virtual fabrics, and the access nodes are responsible forestablishing the virtual fabrics. As such, underlay components of switchfabric 14 may be unware of virtual fabrics. In these examples, accessnodes 17 interface with and utilize switch fabric 14 so as to providefull mesh (any-to-any) interconnectivity between access nodes of anygiven virtual fabric. In this way, the servers connected to any of theaccess nodes forming a given one of virtual fabrics may communicatepacket data for a given packet flow to any other of the servers coupledto the access nodes for that virtual fabric using any of a number ofparallel data paths within switch fabric 14 that interconnect the accessnodes of that virtual fabric. More details of access nodes operating tospray packets within and across virtual overlay networks are availablein U.S. Provisional Patent Application No. 62/638,788, filed Mar. 5,2018, entitled “NETWORK ACCESS NODE VIRTUAL FABRICS CONFIGUREDDYNAMICALLY OVER AN UNDERLAY NETWORK,” the entire content of which isincorporated herein by reference.

Although not shown, data center 10 may also include, for example, one ormore non-edge switches, routers, hubs, gateways, security devices suchas firewalls, intrusion detection, and/or intrusion prevention devices,servers, computer terminals, laptops, printers, databases, wirelessmobile devices such as cellular phones or personal digital assistants,wireless access points, bridges, cable modems, application accelerators,or other network devices.

As one example, each access node group 19 of multiple access nodes 17may be configured as standalone network device, and may be implementedas a two rack unit (2RU) device that occupies two rack units (e.g.,slots) of an equipment rack. In another example, access node 17 may beintegrated within a server, such as a single 1RU server in which fourCPUs are coupled to the forwarding ASICs described herein on a motherboard deployed within a common computing device. In yet another example,one or more of access nodes 17 and servers 12 may be integrated in asuitable size (e.g., 10RU) frame that may, in such an example, become anetwork storage compute unit (NSCU) for data center 10. For example, anaccess node 17 may be integrated within a mother board of a server 12 orotherwise co-located with a server in a single chassis.

The techniques may provide certain advantages. For example, thetechniques may increase significantly the bandwidth utilization of theunderlying switch fabric 14. Moreover, in example implementations, thetechniques may provide full mesh interconnectivity between the serversof the data center and may nevertheless be non-blocking and drop-free.

Although access nodes 17 are described in FIG. 1 with respect to switchfabric 14 of data center 10, in other examples, access nodes may providefull mesh interconnectivity over any packet switched network. Forexample, the packet switched network may include a local area network(LAN), a wide area network (WAN), or a collection of one or morenetworks. The packet switched network may have any topology, e.g., flator multi-tiered, as long as there is full connectivity between theaccess nodes. The packet switched network may use any technology,including IP over Ethernet as well as other technologies. Irrespectiveof the type of packet switched network, in accordance with thetechniques described in this disclosure, access nodes may sprayindividual packets for packet flows between the access nodes and acrossmultiple parallel data paths in the packet switched network and reorderthe packets for delivery to the destinations so as to provide full meshconnectivity.

FIG. 2A is a block diagram illustrating an example optical permutor 40,which may be any of optical permutors 32 of FIG. 1. In this example,optical permutor 40 includes a plurality of bidirectional input ports(P1-P32) that each send and receive respective optical signals. In thisexample, optical permutor 40 includes 32 optical ports with P1-P16 beingaccess node-facing ports for optically coupling to access nodes 17 andports P17-P32 being core switch-facing ports for optically coupling withcore switches 22. In one particular example, each port comprises abidirectional 400 Gigabit optical interface capable of coupling to four100 Gigabit single-mode optical fiber (SMF) pairs, each fiber carryingfour 25G wavelengths λ₁, λ₂, λ₃, λ₄. As such, in this example, each portP1-P32 provides 400 Gigabit optical bandwidth. The described examplearchitecture readily scales and may support, for example, 200 and 400Gigabit fibers carrying four (or more) 50G and 100G wavelengths,respectively.

In the example of FIG. 2A, optical permutor 40 includes four opticalmultiplexors/demultiplexors (“Optics Mux Slice 0-3” in FIG. 2A) 41A-41D(herein, “Optics Mux Slice 41”) having four 400G access node-facingoptical ports 43 and sixteen core switch-facing 100G optical ports 45.As shown in more detail in FIG. 2B, each optics mux slice 41 receivesthe optical signals carried by SMFs for the set of four optical ports43, splits the four wavelengths in the optical signal for each SMF andsprays the wavelengths carried by each SMF in a 4×4 spray across the setof sixteen optical ports 45.

FIG. 2B is a block diagram illustrating in further detail an example ofan optics mux slice 41 of FIG. 2A. In the example of FIG. 2B, eachoptics mux slice 41 includes four optical mux/demux chips 47A-47D(herein, “optical mux/demux chips 47”). Each of the optical mux/demuxchips 47 receives an optical signal from one of the SMFs for each of thedifferent inputs ports (P) serviced by the optical mux slice 41, such asports P1-P4 for optics mux slice 41A of FIG. 2A. Each of the opticalmux/demux chips 47 splits the four wavelengths in the optical signal foreach SMF and sprays the wavelengths carried by each SMF in 4×4 sprayacross a set of four optical ports 49.

For example, in FIG. 2B, each optical communication is designated asλ_(p,w), where the subscript p represents the port and the subscript wrepresents a different wavelength. Thus, using this nomenclature, portP1 of optics mux slice 41 receives a light beam carrying communicationsat n different wavelengths designated λ_(1,1), λ_(1,2), λ_(1,3), andλ_(1,4) where, in this example, n equals 4. Similarly, optical port P2receives a light beam carrying communications at n different wavelengthsdesignated λ_(2,1), λ_(2,2), λ_(2,3), and λ_(2,4). As shown, eachoptical mux/demux chips 47A-47D receive an optical signal carryingλ_(1,1), λ_(1,2), λ_(1,3), and λ_(1,4) from port P1, an optical signalcarrying λ_(2,1), λ_(2,2), λ_(2,3), and λ_(2,4) from port P2, an opticalsignal carrying λ_(3,1), λ_(3,2), λ_(3,3), and λ_(3,4) from port P3 andan optical signal carrying λ_(4,1), λ_(4,2), λ_(4,3), and λ_(4,4) fromport P4. Each of the optical mux/demux chips 47 splits the fourwavelengths in the optical signal for each SMF and sprays thewavelengths carried by each SMF such that optical ports 49 each carry adifferent one of the possible unique permutations of the combinations ofoptical input ports P1-P4 and the optical wavelengths carried by thoseports and where no single optical output port 49 carries multipleoptical communications having the same wavelength. For example, as shownin FIG. 2B, a set of four (4) optical output ports 49 for any givenoptical mux/demux chip 47 may output an optical signal of wavelengthsλ_(1,1), λ_(4,2), λ_(3,3), and λ_(2,4) on a first port, an opticalsignal carrying wavelengths λ_(2,1), λ_(1,2), λ_(4,3), and λ_(3,4) on asecond port, an optical signal carrying λ_(3,1), λ_(2,2), λ_(1,3), andλ_(4,4) on a third optical port and an optical signal carrying λ_(4,1),λ_(3,2), λ_(2,3), and λ_(4,4) on a fourth port.

The following provides a complete example for one implementation ofoptical permutor 40 of FIGS. 1, 2A-2B. In this example, each of portsP1-P32 comprise four separate single mode optical fibers pairs(designated F1-F4 for each port). That is, each port P1-P32 of opticalpermutor 40 comprises an input optical interface configured to receivefour separate fibers, such as a 400G optical interface configured tocouple to and receive optical signals from four separate 100G opticalfibers. In addition, each port P1-P32 of optical permutor 40 comprisesan output optical interface configured to connect to and transmitoptical signals on four separate fibers, such as a 400G opticalinterface configured to receive four separate 100G optical fibers.

Further, each of the four optical fiber pairs for each of input portsP1-P16 is coupled to a different access node 17, thereby providingbidirectional optical connectivity from 64 different access nodes.Moreover, in this example, each access node utilizes four differentwavelengths (L1-L4) for communications associated with servers 12 so asto support parallel communications for up to four servers per accessnode.

Table 1 lists one example configuration for optical permutor 40 foroptical communications in the core-facing direction. That is, Table 1illustrates an example configuration of optical permutor 40 forproducing, on the optical fibers of core-facing output ports P17-P32, aset of 64 unique permutations for combinations of optical input portsP1-P16 and optical wavelengths L1-L4 carried by those input ports, whereno single optical output port carries multiple optical communicationshaving the same wavelength. For example, the first column of Table 1lists the wavelengths L1-L4 carried by the four fibers F1-F4 of eachinput optical interfaces for ports P0-P16 while the right column liststhe unique and non-interfering permutation of input portfiber/wavelength combination output on each optical output interface ofports P17-P32.

TABLE 1 Rack-facing Core-switch facing Output Ports for Optical PermutorInput ports for Optical Permutor (permutation of wavelengths & inputport) Input Port 1: Output Port 17: Fiber 1: P1F1L1-P1F1L4 Fiber 1:P1F1L1, P2F1L2, P3F1L3, P4F1L4 Fiber 2: P1F2L1-P1F2L4 Fiber 2: P5F1L1,P6F1L2, P7F1L3, P8F1L4 Fiber 3: P1F3L1-P1F3L4 Fiber 3: P9F1L1, P10F1L2,P11F1L3, P12F1L4 Fiber 4: P1F4L1-P1F4L4 Fiber 4: P13F1L1, P14F1L2,P15F1L3, P16F1L4 Input Port 2: Output Port 18: Fiber 1: P2F1L1-P2F1L4Fiber 1: P1F2L1, P2F2L2, P3F2L3, P4F2L4 Fiber 2: P2F2L1-P2F2L4 Fiber 2:P5F2L1, P6F2L2, P7F2L3, P8F2L4 Fiber 3: P2F3L1-P2F3L4 Fiber 3: P9F2L1,P10F2L2, P11F2L3, P12F2L4 Fiber 4: P2F4L1-P2F4L4 Fiber 4: P13F2L1,P14F2L2, P15F2L3, P16F2L4 Input Port 3: Output Port 19: Fiber 1:P3F1L1-P3F1L4 Fiber 1: P1F3L1, P2F3L2, P3F3L3, P4F3L4 Fiber 2:P3F2L1-P3F2L4 Fiber 2: P5F3L1, P6F3L2, P7F3L3, P8F3L4 Fiber 3:P3F3L1-P3F3L4 Fiber 3: P9F3L1, P10F3L2, P11F3L3, P12F3L4 Fiber 4:P3F4L1-P3F4L4 Fiber 4: P13F3L1, P14F3L2, P15F3L3, P16F3L4 Input Port 4:Output Port 20: Fiber 1: P4F1L1-P4F1L4 Fiber 1: P1F4L1, P2F4L2, P3F4L3,P4F4L4 Fiber 2: P4F2L1-P4F2L4 Fiber 2: P5F4L1, P6F4L2, P7F4L3, P8F4L4Fiber 3: P4F3L1-P4F3L4 Fiber 3: P9F4L1, P10F4L2, P11F4L3, P12F4L4 Fiber4: P4F4L1-P4F4L4 Fiber 4: P13F4L1, P14F4L2, P15F4L3, P16F4L4 Input Port5: Output Port 21: Fiber 1: P5F1L1-P5F1L4 Fiber 1: P2F1L1, P3F1L2,P4F1L3, P5F1L4 Fiber 2: P5F2L1-P5F2L4 Fiber 2: P6F1L1, P7F1L2, P8F1L3,P9F1L4 Fiber 3: P5F3L1-P5F3L4 Fiber 3: P10F1L1, P11F1L2, P12F1L3,P13F1L4 Fiber 4: P5F4L1-P5F4L4 Fiber 4: P14F1L1, P15F1L2, P16F1L3,P1F1L4 Input Port 6: Output Port 22: Fiber 1: P6F1L1-P6F1L4 Fiber 1:P2F2L1, P3F2L2, P4F2L3, P5F2L4 Fiber 2: P6F2L1-P6F2L4 Fiber 2: P6F2L1,P7F2L2, P8F2L3, P9F2L4 Fiber 3: P6F3L1-P6F3L4 Fiber 3: P10F2L1, P11F2L2,P12F2L3, P13F2L4 Fiber 4: P6F4L1-P6F4L4 Fiber 4: P14F2L1, P15F2L2,P16F2L3, P1F2L4 Input Port 7: Output Port 23: Fiber 1: P7F1L1-P7F1L4Fiber 1: P2F3L1, P3F3L2, P4F3L3, P5F3L4 Fiber 2: P7F2L1-P7F2L4 Fiber 2:P6F3L1, P7F3L2, P8F3L3, P9F3L4 Fiber 3: P7F3L1-P7F3L4 Fiber 3: P10F3L1,P11F3L2, P12F3L3, P13F3L4 Fiber 4: P7F4L1-P7F4L4 Fiber 4: P14F3L1,P15F3L2, P16F3L3, P1F3L4 Input Port 8: Output Port 24: Fiber 1:P8F1L1-P8F1L4 Fiber 1: P2F4L1, P3F4L2, P4F4L3, P5F4L4 Fiber 2:P8F2L1-P8F2L4 Fiber 2: P6F4L1, P7F4L2, P8F4L3, P9F4L4 Fiber 3:P8F3L1-P8F3L4 Fiber 3: P10F4L1, P11F4L2, P12F4L3, P13F4L4 Fiber 4:P8F4L1-P8F4L4 Fiber 4: P14F4L1, P15F4L2, P16F4L3, P1F4L4 Input Port 9:Output Port 25: Fiber 1: P9F1L1-P9F1L4 Fiber 1: P3F1L1, P4F1L2, P5F1L3,P6F1L4 Fiber 2: P9F2L1-P9F2L4 Fiber 2: P7F1L1, P8F1L2, P9F1L3, P10F1L4Fiber 3: P9F3L1-P9F3L4 Fiber 3: P11F1L1, P12F1L2, P13F1L3, P14F1L4 Fiber4: P9F4L1-P9F4L4 Fiber 4: P15F1L1, P16F1L2, P1F1L3, P2F1L4 Input Port10: Output Port 26: Fiber 1: P10F1L1-P10F1L4 Fiber 1: P3F2L1, P4F2L2,P5F2L3, P6F2L4 Fiber 2: P10F2L1-P10F2L4 Fiber 2: P7F2L1, P8F2L2, P9F2L3,P10F2L4 Fiber 3: P10F3L1-P10F3L4 Fiber 3: P11F2L1, P12F2L2, P13F2L3,P14F2L4 Fiber 4: P10F4L1-P10F4L4 Fiber 4: P15F2L1, P16F2L2, P1F2L3,P2F2L4 Input Port 11: Output Port 27: Fiber 1: P11F1L1-P11F1L4 Fiber 1:P3F3L1, P4F3L2, P5F3L3, P6F3L4 Fiber 2: P11F2L1-P11F2L4 Fiber 2: P7F3L1,P8F3L2, P9F3L3, P10F3L4 Fiber 3: P11F3L1-P11F3L4 Fiber 3: P11F3L1,P12F3L2, P13F3L3, P14F3L4 Fiber 4: P11F4L1-P11F4L4 Fiber 4: P15F3L1,P16F3L2, P1F3L3, P2F3L4 Input Port 12: Output Port 28: Fiber 1:P12F1L1-P12F1L4 Fiber 1: P3F4L1, P4F4L2, P5F4L3, P6F4L4 Fiber 2:P12F2L1-P12F2L4 Fiber 2: P7F4L1, P8F4L2, P9F4L3, P10F4L4 Fiber 3:P12F3L1-P12F3L4 Fiber 3: P11F4L1, P12F4L2, P13F4L3, P14F4L4 Fiber 4:P12F4L1-P12F4L4 Fiber 4: P15F4L1, P16F4L2, P1F4L3, P2F4L4 Input Port 13:Output Port 29: Fiber 1: P13F1L1-P13F1L4 Fiber 1: P4F1L1, P5F1L2,P6F1L3, P7F1L4 Fiber 2: P13F2L1-P13F2L4 Fiber 2: P8F1L1, P9F1L2,P10F1L3, P11F1L4 Fiber 3: P13F3L1-P13F3L4 Fiber 3: P12F1L1, P13F1L2,P14F1L3, P15F1L4 Fiber 4: P13F4L1-P13F4L4 Fiber 4: P16F1L1, P1F1L2,P2F1L3, P3F1L4 Input Port 14: Output Port 30: Fiber 1: P14F1L1-P14F1L4Fiber 1: P4F2L1, P5F2L2, P6F2L3, P7F2L4 Fiber 2: P14F2L1-P14F2L4 Fiber2: P8F2L1, P9F2L2, P10F2L3, P11F2L4 Fiber 3: P14F3L1-P14F3L4 Fiber 3:P12F2L1, P13F2L2, P14F2L3, P15F2L4 Fiber 4: P14F4L1-P14F4L4 Fiber 4:P16F2L1, P1F2L2, P2F2L3, P3F2L4 Input Port 15: Output Port 31: Fiber 1:P15F1L1-P15F1L4 Fiber 1: P4F3L1, P5F3L2, P6F3L3, P7F3L4 Fiber 2:P15F2L1-P15F2L4 Fiber 2: P8F3L1, P9F3L2, P10F3L3, P11F3L4 Fiber 3:P15F3L1-P15F3L4 Fiber 3: P12F3L1, P13F3L2, P14F3L3, P15F3L4 Fiber 4:P15F4L1-P15F4L4 Fiber 4: P16F3L1, P1F3L2, P2F3L3, P3F3L4 Input Port 16:Output Port 32: Fiber 1: P16F1L1-P16F1L4 Fiber 1: P4F4L1, P5F4L2,P6F4L3, P7F4L4 Fiber 2: P16F2L1-P16F2L4 Fiber 2: P8F4L1, P9F4L2,P10F4L3, P11F4L4 Fiber 3: P16F3L1-P16F3L4 Fiber 3: P12F4L1, P13F4L2,P14F4L3, P15F4L4 Fiber 4: P16F4L1-P16F4L4 Fiber 4: P16F4L1, P1F4L2,P2F4L3, P3F4L4

Continuing the example, Table 2 lists an example configuration foroptical permutor 40 with respect to optical communications in thereverse, downstream direction, i.e., from core switches 22 to accessnodes 17. That is, Table 2 illustrates an example configuration ofoptical permutor 40 for producing, on the optical fibers of rack-facingoutput ports P1-P16, a set of 64 unique permutations for combinations ofcore-facing input ports P16-P32 and optical wavelengths L1-L4 carried bythose input ports, where no single optical output port carries multipleoptical communications having the same wavelength.

TABLE 2 Access node-facing Output Ports for Core switch-facing InputPorts for Optical Permutor Optical Permutor (permutation of wavelengths& input port) Input Port 17: Output Port 1: Fiber 1: P17F1L1-P17F1L4Fiber 1: P17F1L1, P18F1L2, P19F1L3, P20F1L4 Fiber 2: P17F2L1-P17F2L4Fiber 2: P21F1L1, P22F1L2, P23F1L3, P24F1L4 Fiber 3: P17F3L1-P17F3L4Fiber 3: P25F1L1, P26F1L2, P27F1L3, P28F1L4 Fiber 4: P17F4L1-P17F4L4Fiber 4: P29F1L1, P30F1L2, P31F1L3, P32F1L4 Input Port 18: Output Port2: Fiber 1: P18F1L1-P18F1L4 Fiber 1: P17F2L1, P18F2L2, P19F2L3, P20F2L4Fiber 2: P18F2L1-P18F2L4 Fiber 2: P21F2L1, P22F2L2, P23F2L3, P24F2L4Fiber 3: P18F3L1-P18F3L4 Fiber 3: P25F2L1, P26F2L2, P27F2L3, P28F2L4Fiber 4: P18F4L1-P18F4L4 Fiber 4: P29F2L1, P30F2L2, P31F2L3, P32F2L4Input Port 19: Output Port 3: Fiber 1: P19F1L1-P19F1L4 Fiber 1: P17F3L1,P18F3L2, P19F3L3, P20F3L4 Fiber 2: P19F2L1-P19F2L4 Fiber 2: P21F3L1,P22F3L2, P23F3L3, P24F3L4 Fiber 3: P19F3L1-P19F3L4 Fiber 3: P25F3L1,P26F3L2, P27F3L3, P28F3L4 Fiber 4: P19F4L1-P19F4L4 Fiber 4: P29F3L1,P30F3L2, P31F3L3, P32F3L4 Input Port 20: Output Port 4: Fiber 1:P20F1L1-P20F1L4 Fiber 1: P17F4L1, P18F4L2, P19F4L3, P20F4L4 Fiber 2:P20F2L1-P20F2L4 Fiber 2: P21F4L1, P22F4L2, P23F4L3, P24F4L4 Fiber 3:P20F3L1-P20F3L4 Fiber 3: P25F4L1, P26F4L2, P27F4L3, P28F4L4 Fiber 4:P20F4L1-P20F4L4 Fiber 4: P29F4L1, P30F4L2, P31F4L3, P32F4L4 Input Port21: Output Port 5: Fiber 1: P21F1L1-P21F1L4 Fiber 1: P18F1L1, P19F1L2,P20F1L3, P21F1L4 Fiber 2: P21F2L1-P21F2L4 Fiber 2: P22F1L1, P23F1L2,P24F1L3, P25F1L4 Fiber 3: P21F3L1-P21F3L4 Fiber 3: P26F1L1, P27F1L2,P28F1L3, P29F1L4 Fiber 4: P21F4L1-P21F4L4 Fiber 4: P30F1L1, P31F1L2,P32F1L3, P17F1L4 Input Port 22: Output Port 6: Fiber 1: P22F1L1-P22F1L4Fiber 1: P18F2L1, P19F2L2, P20F2L3, P21F2L4 Fiber 2: P22F2L1-P22F2L4Fiber 2: P22F2L1, P23F2L2, P24F2L3, P25F2L4 Fiber 3: P22F3L1-P22F3L4Fiber 3: P26F2L1, P27F2L2, P28F2L3, P29F2L4 Fiber 4: P22F4L1-P22F4L4Fiber 4: P30F2L1, P31F2L2, P32F2L3, P17F2L4 Input Port 23: Output Port7: Fiber 1: P23F1L1-P23F1L4 Fiber 1: P18F3L1, P19F3L2, P20F3L3, P21F3L4Fiber 2: P23F2L1-P23F2L4 Fiber 2: P22F3L1, P23F3L2, P24F3L3, P25F3L4Fiber 3: P23F3L1-P23F3L4 Fiber 3: P26F3L1, P27F3L2, P28F3L3, P29F3L4Fiber 4: P23F4L1-P23F4L4 Fiber 4: P30F3L1, P31F3L2, P32F3L3, P17F3L4Input Port 24: Output Port 8: Fiber 1: P24F1L1-P24F1L4 Fiber 1: P18F2L1,P19F2L2, P20F2L3, P21F2L4 Fiber 2: P24F2L1-P24F2L4 Fiber 2: P22F2L1,P23F2L2, P24F2L3, P25F2L4 Fiber 3: P24F3L1-P24F3L4 Fiber 3: P26F2L1,P27F2L2, P28F2L3, P29F2L4 Fiber 4: P24F4L1-P24F4L4 Fiber 4: P30F2L1,P31F2L2, P32F2L3, P17F2L4 Input Port 25: Output Port 9: Fiber 1:P25F1L1-P25F1L4 Fiber 1: P19F1L1, P20F1L2, P21F1L3, P22F1L4 Fiber 2:P25F2L1-P25F2L4 Fiber 2: P23F1L1, P24F1L2, P25F1L3, P26F1L4 Fiber 3:P25F3L1-P25F3L4 Fiber 3: P27F1L1, P28F1L2, P29F1L3, P30F1L4 Fiber 4:P25F4L1-P25F4L4 Fiber 4: P31F1L1, P32F1L2, P17F1L3, P18F1L4 Input Port26: Output Port 10: Fiber 1: P26F1L1-P26F1L4 Fiber 1: P19F2L1, P20F2L2,P21F2L3, P22F2L4 Fiber 2: P26F2L1-P26F2L4 Fiber 2: P23F2L1, P24F2L2,P25F2L3, P26F2L4 Fiber 3: P26F3L1-P26F3L4 Fiber 3: P27F2L1, P28F2L2,P29F2L3, P30F2L4 Fiber 4: P26F4L1-P26F4L4 Fiber 4: P31F2L1, P32F2L2,P17F2L3, P18F2L4 Input Port 27: Output Port 11: Fiber 1: P27F1L1-P27F1L4Fiber 1: P19F3L1, P20F3L2, P21F3L3, P22F3L4 Fiber 2: P27F2L1-P27F2L4Fiber 2: P23F3L1, P24F3L2, P25F3L3, P26F3L4 Fiber 3: P27F3L1-P27F3L4Fiber 3: P27F3L1, P28F3L2, P29F3L3, P30F3L4 Fiber 4: P27F4L1-P27F4L4Fiber 4: P31F3L1, P32F3L2, P17F3L3, P18F3L4 Input Port 28: Output Port12: Fiber 1: P28F1L1-P28F1L4 Fiber 1: P19F4L1, P20F4L2, P21F4L3, P22F4L4Fiber 2: P28F2L1-P28F2L4 Fiber 2: P23F4L1, P24F4L2, P25F4L3, P26F4L4Fiber 3: P28F3L1-P28F3L4 Fiber 3: P27F4L1, P28F4L2, P29F4L3, P30F4L4Fiber 4: P28F4L1-P28F4L4 Fiber 4: P31F4L1, P32F4L2, P17F4L3, P18F4L4Input Port 29: Output Port 13: Fiber 1: P29F1L1-P29F1L4 Fiber 1:P20F1L1, P21F1L2, P22F1L3, P23F1L4 Fiber 2: P29F2L1-P29F2L4 Fiber 2:P24F1L1, P25F1L2, P26F1L3, P27F1L4 Fiber 3: P29F3L1-P29F3L4 Fiber 3:P28F1L1, P29F1L2, P30F1L3, P31F1L4 Fiber 4: P29F4L1-P29F4L4 Fiber 4:P32F1L1, P17F1L2, P18F1L3, P19F1L4 Input Port 30: Output Port 14: Fiber1: P30F1L1-P30F1L4 Fiber 1: P20F2L1, P21F2L2, P22F2L3, P23F2L4 Fiber 2:P30F2L1-P30F2L4 Fiber 2: P24F2L1, P25F2L2, P26F2L3, P27F2L4 Fiber 3:P30F3L1-P30F3L4 Fiber 3: P28F2L1, P29F2L2, P30F2L3, P31F2L4 Fiber 4:P30F4L1-P30F4L4 Fiber 4: P32F2L1, P17F2L2, P18F2L3, P19F2L4 Input Port31: Output Port 15: Fiber 1: P31F1L1-P31F1L4 Fiber 1: P20F3L1, P21F3L2,P22F3L3, P23F3L4 Fiber 2: P31F2L1-P31F2L4 Fiber 2: P24F3L1, P25F3L2,P26F3L3, P27F3L4 Fiber 3: P31F3L1-P31F3L4 Fiber 3: P28F3L1, P29F3L2,P30F3L3, P31F3L4 Fiber 4: P31F4L1-P31F4L4 Fiber 4: P32F3L1, P17F3L2,P18F3L3, P19F3L4 Input Port 32: Output Port 16: Fiber 1: P32F1L1-P32F1L4Fiber 1: P20F4L1, P21F4L2, P22F4L3, P23F4L4 Fiber 2: P32F2L1-P32F2L4Fiber 2: P24F4L1, P25F4L2, P26F4L3, P27F4L4 Fiber 3: P32F3L1-P32F3L4Fiber 3: P28F4L1, P29F4L2, P30F4L3, P31F4L4 Fiber 4: P32F4L1-P32F4L4Fiber 4: P32F4L1, P17F4L2, P18F4L3, P19F4L4

Table 3 lists a second example configuration for optical permutor 40 foroptical communications in the core-facing direction. As with Table 1above, Table 3 illustrates an example configuration of optical permutor40 for producing, on the optical fibers of core-facing output portsP17-P32, a set of 64 unique permutations for combinations of opticalinput ports P1-P16 and optical wavelengths L1-L4 carried by those inputports, where no single optical output port carries multiple opticalcommunications having the same wavelength. Similar to Table 1 above, thefirst column of Table 3 lists the wavelengths L1-L4 carried by the fourfibers F1-F4 of each input optical interfaces for ports P0-P16 while theright column lists another example of unique and non-interferingpermutation of input port fiber/wavelength combination output on eachoptical output interface of ports P17-P32.

TABLE 3 Rack-facing Core-switch facing Output Ports for Optical PermutorInput ports for Optical Permutor (permutation of wavelengths & inputport) Input Port 1: Output Port 17: Fiber 1: P1F1L1-P1F1L4 Fiber 1:P1F1L1, P2F1L2, P3F1L3, P4F1L4 Fiber 2: P1F2L1-P1F2L4 Fiber 2: P5F1L1,P6F1L2, P7F1L3, P8F1L4 Fiber 3: P1F3L1-P1F3L4 Fiber 3: P9F1L1, P10F1L2,P11F1L3, P12F1L4 Fiber 4: P1F4L1-P1F4L4 Fiber 4: P13F1L1, P14F1L2,P15F1L3, P16F1L4 Input Port 2: Output Port 18: Fiber 1: P2F1L1-P2F1L4Fiber 1: P2F1L1, P3F1L2, P4F1L3, P1F1L4 Fiber 2: P2F2L1-P2F2L4 Fiber 2:P6F1L1, P7F1L2, P8F1L3, P5F1L4 Fiber 3: P2F3L1-P2F3L4 Fiber 3: P10F1L1,P11F1L2, P12F1L3, P9F1L4 Fiber 4: P2F4L1-P2F4L4 Fiber 4: P14F1L1,P15F1L2, P16F1L3, P13F1L4 Input Port 3: Output Port 19: Fiber 1:P3F1L1-P3F1L4 Fiber 1: P3F1L1, P4F1L2, P1F1L3, P2F1L4 Fiber 2:P3F2L1-P3F2L4 Fiber 2: P7F1L1, P8F1L2, P5F1L3, P6F1L4 Fiber 3:P3F3L1-P3F3L4 Fiber 3: P11F1L1, P12F1L2, P9F1L3, P10F1L4 Fiber 4:P3F4L1-P3F4L4 Fiber 4: P15F1L1, P16F1L2, P13F1L3, P14F1L4 Input Port 4:Output Port 20: Fiber 1: P4F1L1-P4F1L4 Fiber 1: P4F1L1, P1F1L2, P2F1L3,P3F1L4 Fiber 2: P4F2L1-P4F2L4 Fiber 2: P8F1L1, P5F1L2, P6F1L3, P7F1L4Fiber 3: P4F3L1-P4F3L4 Fiber 3: P12F1L1, P9F1L2, P10F1L3, P11F1L4 Fiber4: P4F4L1-P4F4L4 Fiber 4: P16F1L1, P13F1L2, P14F1L3, P15F1L4 Input Port5: Output Port 21: Fiber 1: P5F1L1-P5F1L4 Fiber 1: P1F2L1, P2F2L2,P3F2L3, P4F2L4 Fiber 2: P5F2L1-P5F2L4 Fiber 2: P5F2L1, P6F2L2, P7F2L3,P8F2L4 Fiber 3: P5F3L1-P5F3L4 Fiber 3: P9F2L1, P10F2L2, P11F2L3, P12F2L4Fiber 4: P5F4L1-P5F4L4 Fiber 4: P13F2L1, P14F2L2, P15F2L3, P6F2L4 InputPort 6: Output Port 22: Fiber 1: P6F1L1-P6F1L4 Fiber 1: P2F2L1, P3F2L2,P4F2L3, P1F2L4 Fiber 2: P6F2L1-P6F2L4 Fiber 2: P6F2L1, P7F2L2, P8F2L3,P5F2L4 Fiber 3: P6F3L1-P6F3L4 Fiber 3: P10F2L1, P11F2L2, P12F2L3, P9F2L4Fiber 4: P6F4L1-P6F4L4 Fiber 4: P14F2L1, P15F2L2, P16F2L3, P13F2L4 InputPort 7: Output Port 23: Fiber 1: P7F1L1-P7F1L4 Fiber 1: P3F2L1, P4F2L2,P1F2L3, P2F2L4 Fiber 2: P7F2L1-P7F2L4 Fiber 2: P7F2L1, P8F2L2, P5F2L3,P6F2L4 Fiber 3: P7F3L1-P7F3L4 Fiber 3: P11F2L1, P12F2L2, P9F2L3, P10F2L4Fiber 4: P7F4L1-P7F4L4 Fiber 4: P15F2L1, P16F2L2, P13F2L3, P14F2L4 InputPort 8: Output Port 24: Fiber 1: P8F1L1-P8F1L4 Fiber 1: P4F2L1, P1F2L2,P2F2L3, P3F2L4 Fiber 2: P8F2L1-P8F2L4 Fiber 2: P8F2L1, P5F2L2, P6F2L3,P7F2L4 Fiber 3: P8F3L1-P8F3L4 Fiber 3: P12F2L1, P9F2L2, P10F2L3, P11F2L4Fiber 4: P8F4L1-P8F4L4 Fiber 4: P16F2L1, P13F2L2, P14F2L3, P15F2L4 InputPort 9: Output Port 25: Fiber 1: P9F1L1-P9F1L4 Fiber 1: P1F3L1, P2F3L2,P3F3L3, P4F3L4 Fiber 2: P9F2L1-P9F2L4 Fiber 2: P5F3L1, P6F3L2, P7F3L3,P8F3L4 Fiber 3: P9F3L1-P9F3L4 Fiber 3: P9F3L1, P10F3L2, P11F3L3, P12F3L4Fiber 4: P9F4L1-P9F4L4 Fiber 4: P13F3L1, P14F3L2, P15F3L3, P16F3L4 InputPort 10: Output Port 26: Fiber 1: P10F1L1-P10F1L4 Fiber 1: P2F3L1,P3F3L2, P4F3L3, P1F3L4 Fiber 2: P10F2L1-P10F2L4 Fiber 2: P6F3L1, P7F3L2,P8F3L3, P5F3L4 Fiber 3: P10F3L1-P10F3L4 Fiber 3: P10F3L1, P11F3L2,P12F3L3, P9F3L4 Fiber 4: P10F4L1-P10F4L4 Fiber 4: P14F3L1, P15F3L2,P16F3L3, P13F3L4 Input Port 11: Output Port 27: Fiber 1: P11F1L1-P11F1L4Fiber 1: P3F3L1, P4F3L2, P1F3L3, P2F3L4 Fiber 2: P11F2L1-P11F2L4 Fiber2: P7F3L1, P8F3L2, P5F3L3, P6F3L4 Fiber 3: P11F3L1-P11F3L4 Fiber 3:P11F3L1, P12F3L2, P9F3L3, P10F3L4 Fiber 4: P11F4L1-P11F4L4 Fiber 4:P15F3L1, P16F3L2, P13F3L3, P14F3L4 Input Port 12: Output Port 28: Fiber1: P12F1L1-P12F1L4 Fiber 1: P4F3L1, P1F3L2, P2F3L3, P3F3L4 Fiber 2:P12F2L1-P12F2L4 Fiber 2: P8F3L1, P5F3L2, P6F3L3, P7F3L4 Fiber 3:P12F3L1-P12F3L4 Fiber 3: P12F3L1, P9F3L2, P10F3L3, P11F3L4 Fiber 4:P12F4L1-P12F4L4 Fiber 4: P16F3L1, P13F3L2, P14F3L3, P15F3L4 Input Port13: Output Port 29: Fiber 1: P13F1L1-P13F1L4 Fiber 1: P1F4L1, P2F4L2,P3F4L3, P4F4L4 Fiber 2: P13F2L1-P13F2L4 Fiber 2: P5F4L1, P6F4L2, P7F4L3,P8F4L4 Fiber 3: P13F3L1-P13F3L4 Fiber 3: P9F4L1, P10F4L2, P11F4L3,P12F4L4 Fiber 4: P13F4L1-P13F4L4 Fiber 4: P13F4L1, P14F4L2, P15F4L3,P16F4L4 Input Port 14: Output Port 30: Fiber 1: P14F1L1-P14F1L4 Fiber 1:P2F4L1, P3F4L2, P4F4L3, P1F4L4 Fiber 2: P14F2L1-P14F2L4 Fiber 2: P6F4L1,P7F4L2, P8F4L3, P5F4L4 Fiber 3: P14F3L1-P14F3L4 Fiber 3: P10F4L1,P11F4L2, P12F4L3, P9F4L4 Fiber 4: P14F4L1-P14F4L4 Fiber 4: P14F4L1,P15F4L2, P16F4L3, P13F4L4 Input Port 15: Output Port 31: Fiber 1:P15F1L1-P15F1L4 Fiber 1: P3F4L1, P4F4L2, P1F4L3, P2F4L4 Fiber 2:P15F2L1-P15F2L4 Fiber 2: P7F4L1, P8F4L2, P5F4L3, P6F4L4 Fiber 3:P15F3L1-P15F3L4 Fiber 3: P11F4L1, P12F4L2, P9F4L3, P10F4L4 Fiber 4:P15F4L1-P15F4L4 Fiber 4: P15F4L1, P16F4L2, P13F4L3, P14F4L4 Input Port16: Output Port 32: Fiber 1: P16F1L1-P16F1L4 Fiber 1: P4F4L1, P1F4L2,P2F4L3, P3F4L4 Fiber 2: P16F2L1-P16F2L4 Fiber 2: P8F4L1, P5F4L2, P6F4L3,P7F4L4 Fiber 3: P16F3L1-P16F3L4 Fiber 3: P12F4L1, P9F4L2, P10F4L3,P11F4L4 Fiber 4: P16F4L1-P16F4L4 Fiber 4: P16F4L1, P13F4L2, P14F4L3,P15F4L4

Continuing the example, Table 4 lists another example configuration foroptical permutor 40 with respect to optical communications in thereverse, downstream direction, i.e., from core switches 22 to accessnodes 17. Like Table 2 above, Table 4 illustrates another exampleconfiguration of optical permutor 40 for producing, on the opticalfibers of rack-facing output ports P1-P16, a set of 64 uniquepermutations for combinations of core-facing input ports P16-P32 andoptical wavelengths L1-L4 carried by those input ports, where no singleoptical output port carries multiple optical communications having thesame wavelength.

TABLE 4 Access node-facing Output Ports for Core switch-facing InputPorts for Optical Permutor Optical Permutor (permutation of wavelengths& input port) Input Port 17: Output Port 1: Fiber 1: P17F1L1-P17F1L4Fiber 1: P17F1L1, P18F1L2, P19F1L3, P20F1L4 Fiber 2: P17F2L1-P17F2L4Fiber 2: P21F1L1, P22F1L2, P23F1L3, P24F1L4 Fiber 3: P17F3L1-P17F3L4Fiber 3: P25F1L1, P26F1L2, P27F1L3, P28F1L4 Fiber 4: P17F4L1-P17F4L4Fiber 4: P29F1L1, P30F1L2, P31F1L3, P32F1L4 Input Port 18: Output Port2: Fiber 1: P18F1L1-P18F1L4 Fiber 1: P18F1L1, P19F1L2, P20F1L3, P17F1L4Fiber 2: P18F2L1-P18F2L4 Fiber 2: P22F1L1, P23F1L2, P24F1L3, P21F1L4Fiber 3: P18F3L1-P18F3L4 Fiber 3: P26F1L1, P27F1L2, P28F1L3, P25F1L4Fiber 4: P18F4L1-P18F4L4 Fiber 4: P30F1L1, P31F1L2, P32F1L3, P29F1L4Input Port 19: Output Port 3: Fiber 1: P19F1L1-P19F1L4 Fiber 1: P19F1L1,P20F1L2, P17F1L3, P18F1L4 Fiber 2: P19F2L1-P19F2L4 Fiber 2: P23F1L1,P24F1L2, P21F1L3, P22F1L4 Fiber 3: P19F3L1-P19F3L4 Fiber 3: P27F1L1,P28F1L2, P25F1L3, P26F1L4 Fiber 4: P19F4L1-P19F4L4 Fiber 4: P31F1L1,P32F1L2, P29F1L3, P30F1L4 Input Port 20: Output Port 4: Fiber 1:P20F1L1-P20F1L4 Fiber 1: P20F1L1, P17F1L2, P18F1L3, P19F1L4 Fiber 2:P20F2L1-P20F2L4 Fiber 2: P24F1L1, P21F1L2, P22F1L3, P23F1L4 Fiber 3:P20F3L1-P20F3L4 Fiber 3: P28F1L1, P25F1L2, P26F1L3, P27F1L4 Fiber 4:P20F4L1-P20F4L4 Fiber 4: P32F1L1, P29F1L2, P30F1L3, P31F1L4 Input Port21: Output Port 5: Fiber 1: P21F1L1-P21F1L4 Fiber 1: P17F2L1, P18F2L2,P19F2L3, P20F2L4 Fiber 2: P21F2L1-P21F2L4 Fiber 2: P21F2L1, P22F2L2,P23F2L3, P24F2L4 Fiber 3: P21F3L1-P21F3L4 Fiber 3: P25F2L1, P26F2L2,P27F2L3, P28F2L4 Fiber 4: P21F4L1-P21F4L4 Fiber 4: P29F2L1, P30F2L2,P31F2L3, P32F2L4 Input Port 22: Output Port 6: Fiber 1: P22F1L1-P22F1L4Fiber 1: P18F2L1, P19F2L2, P20F2L3, P17F2L4 Fiber 2: P22F2L1-P22F2L4Fiber 2: P22F2L1, P23F2L2, P24F2L3, P21F2L4 Fiber 3: P22F3L1-P22F3L4Fiber 3: P26F2L1, P27F2L2, P28F2L3, P25F2L4 Fiber 4: P22F4L1-P22F4L4Fiber 4: P30F2L1, P31F2L2, P32F2L3, P29F2L4 Input Port 23: Output Port7: Fiber 1: P23F1L1-P23F1L4 Fiber 1: P19F2L1, P20F2L2, P17F2L3, P18F2L4Fiber 2: P23F2L1-P23F2L4 Fiber 2: P23F2L1, P24F2L2, P21F2L3, P22F2L4Fiber 3: P23F3L1-P23F3L4 Fiber 3: P27F2L1, P28F2L2, P25F2L3, P26F2L4Fiber 4: P23F4L1-P23F4L4 Fiber 4: P31F2L1, P32F2L2, P29F2L3, P30F2L4Input Port 24: Output Port 8: Fiber 1: P24F1L1-P24F1L4 Fiber 1: P20F2L1,P17F2L2, P18F2L3, P19F2L4 Fiber 2: P24F2L1-P24F2L4 Fiber 2: P24F2L1,P21F2L2, P22F2L3, P23F2L4 Fiber 3: P24F3L1-P24F3L4 Fiber 3: P28F2L1,P25F2L2, P26F2L3, P27F2L4 Fiber 4: P24F4L1-P24F4L4 Fiber 4: P32F2L1,P29F2L2, P30F2L3, P31F2L4 Input Port 25: Output Port 9: Fiber 1:P25F1L1-P25F1L4 Fiber 1: P17F3L1, P18F3L2, P19F3L3, P20F3L4 Fiber 2:P25F2L1-P25F2L4 Fiber 2: P21F3L1, P22F3L2, P23F3L3, P24F3L4 Fiber 3:P25F3L1-P25F3L4 Fiber 3: P25F3L1, P26F3L2, P27F3L3, P28F3L4 Fiber 4:P25F4L1-P25F4L4 Fiber 4: P29F3L1, P30F3L2, P31F3L3, P32F3L4 Input Port26: Output Port 10: Fiber 1: P26F1L1-P26F1L4 Fiber 1: P18F3L1, P19F3L2,P20F3L3, P17F3L4 Fiber 2: P26F2L1-P26F2L4 Fiber 2: P22F3L1, P23F3L2,P24F3L3, P21F3L4 Fiber 3: P26F3L1-P26F3L4 Fiber 3: P26F3L1, P27F3L2,P28F3L3, P25F3L4 Fiber 4: P26F4L1-P26F4L4 Fiber 4: P30F3L1, P31F3L2,P32F3L3, P29F3L4 Input Port 27: Output Port 11: Fiber 1: P27F1L1-P27F1L4Fiber 1: P19F3L1, P20F3L2, P17F3L3, P18F3L4 Fiber 2: P27F2L1-P27F2L4Fiber 2: P23F3L1, P24F3L2, P21F3L3, P22F3L4 Fiber 3: P27F3L1-P27F3L4Fiber 3: P27F3L1, P28F3L2, P25F3L3, P26F3L4 Fiber 4: P27F4L1-P27F4L4Fiber 4: P31F3L1, P32F3L2, P29F3L3, P30F3L4 Input Port 28: Output Port12: Fiber 1: P28F1L1-P28F1L4 Fiber 1: P20F3L1, P17F3L2, P18F3L3, P18F3L4Fiber 2: P28F2L1-P28F2L4 Fiber 2: P24F3L1, P21F3L2, P22F3L3, P23F3L4Fiber 3: P28F3L1-P28F3L4 Fiber 3: P28F3L1, P25F3L2, P26F3L3, P27F3L4Fiber 4: P28F4L1-P28F4L4 Fiber 4: P32F3L1, P29F3L2, P30F3L3, P31F3L4Input Port 29: Output Port 13: Fiber 1: P29F1L1-P29F1L4 Fiber 1:P17F4L1, P18F4L2, P19F4L3, P20F4L4 Fiber 2: P29F2L1-P29F2L4 Fiber 2:P21F4L1, P22F4L2, P23F4L3, P24F4L4 Fiber 3: P29F3L1-P29F3L4 Fiber 3:P25F4L1, P26F4L2, P27F4L3, P28F4L4 Fiber 4: P29F4L1-P29F4L4 Fiber 4:P29F4L1, P30F4L2, P31F4L3, P32F4L4 Input Port 30: Output Port 14: Fiber1: P30F1L1-P30F1L4 Fiber 1: P18F4L1, P19F4L2, P20F4L3, P17F4L4 Fiber 2:P30F2L1-P30F2L4 Fiber 2: P22F4L1, P23F4L2, P24F4L3, P21F4L4 Fiber 3:P30F3L1-P30F3L4 Fiber 3: P26F4L1, P27F4L2, P28F4L3, P25F4L4 Fiber 4:P30F4L1-P30F4L4 Fiber 4: P30F4L1, P31F4L2, P32F4L3, P29F4L4 Input Port31: Output Port 15: Fiber 1: P31F1L1-P31F1L4 Fiber 1: P19F4L1, P20F4L2,P17F4L3, P18F4L4 Fiber 2: P31F2L1-P31F2L4 Fiber 2: P23F4L1, P24F4L2,P21F4L3, P22F4L4 Fiber 3: P31F3L1-P31F3L4 Fiber 3: P27F4L1, P28F4L2,P25F4L3, P26F4L4 Fiber 4: P31F4L1-P31F4L4 Fiber 4: P31F4L1, P32F4L2,P29F4L3, P30F4L4 Input Port 32: Output Port 16: Fiber 1: P32F1L1-P32F1L4Fiber 1: P20F4L1, P17F4L2, P18F4L3, P19F4L4 Fiber 2: P32F2L1-P32F2L4Fiber 2: P24F4L1, P21F4L2, P22F4L3, P23F4L4 Fiber 3: P32F3L1-P32F3L4Fiber 3: P28F4L1, P25F4L2, P26F4L3, P27F4L4 Fiber 4: P32F4L1-P32F4L4Fiber 4: P32F4L1, P29F4L2, P30F4L3, P31F4L4

FIG. 3A is a block diagram illustrating an example optical permutor 50,which may be any of optical permutors 32 of FIG. 1. In this example,optical permutor 50 includes a plurality of input ports 52A-52N (herein,“input ports 52”) to receive respective optical signals, each of theoptical signals carrying communications at a set of n wavelengths. Eachcommunication is designated as λ_(p,w), where the subscript p representsthe port and the subscript w represents with wavelength. Thus, usingthis nomenclature, optical input 52A receives a light beam carryingcommunications at n different wavelengths designated λ_(1,1), λ_(1,2), .. . , λ_(1,n). Similarly, optical input 52B receives a light beamcarrying communications at n different wavelengths designated λ_(2,1),λ_(2,2), . . . λ_(2,n).

Optical permutor 50 includes a respective one of optical demultiplexers60A-60N (herein, “optical demuxes 60”) for each optical input interface52, where the optical demultiplexer is configured to demultiplex theoptical communications for a given optical input onto internal opticalpathways 64 based on the bandwidth of the optical communications. Forexample, optical demux 60A separates the optical communications receivedon optical input interface 52A onto a set of internal optical pathways64A based on wavelengths λ_(1,1), λ_(1,2), . . . λ_(1,n). Optical demux60B separates the optical communications received on optical inputinterface 52B onto a set of internal optical pathways 64B based onwavelengths λ_(2,1), λ_(2,2), . . . , λ_(2,n). Each optical demux 60operates in a similar fashion to separate the optical communicationsreceived from the receptive input optical interface 52 so as to directthe optical communications through internal optical pathways 64 towardoptical output ports 54A-54N (herein, “optical output ports 54”).

Optical permutor 50 includes a respective one of optical multiplexers62A-62N (herein, “optical muxes 62”) for each optical output port 54,where the optical multiplexer receives as input optical signals fromoptical pathways 64 that lead to each optical demux 64. In other words,optical pathways 64 internal to optical permutor 50 provide a full-meshof N² optical interconnects between optical demuxes 60 and optical muxes62. Each optical multiplexer 62 receives N optical pathways as input andcombines the optical signals carried by the N optical pathways into asingle optical signal for output onto a respective optical fiber.

Moreover, optical demuxes 60 are each configured such that opticalcommunications received from input interface ports 52 are “permuted”across optical output ports 54 based on wavelength so as to providefull-mesh connectivity between the ports and in a way that ensuresoptical interference is avoided. That is, each optical demux 60 isconfigured to ensure that each optical output port 54 receives adifferent one of the possible unique permutations of the combinations ofoptical input ports 52 and the optical frequencies carried by thoseports and where no single optical output port 54 carries communicationshaving the same wavelength.

For example, optical demux 60A may be configured to direct the opticalsignal having wavelength λ_(1,1) to optical mux 62A, wavelength λ_(1,2)to optical mux 62B, wavelength λ_(1,3) to optical mux 62C, . . . andwavelength λ_(1,n) to optical mux 62N. Optical demux 60B is configuredto deliver a different (second) permutation of optical signals byoutputting wavelength λ_(2,n) to optical mux 62A, wavelength λ_(2,1) tooptical mux 62B, wavelength λ_(2,2) to optical mux 62C, . . . andwavelength λ_(2,n-1) to optical mux 62N. Optical demux 60C is configuredto deliver a different (third) permutation of optical signals byoutputting wavelength λ_(3,n-1) to optical mux 62A, wavelength λ_(3,n-2)to optical mux 62B, wavelength λ_(3,n-3) to optical mux 62C, . . . andwavelength λ_(3,n-2) to optical mux 62N. This example configurationpattern continues through optical demux 60N, which is configured todeliver a different (N^(th)) permutation of optical signals byoutputting wavelength λ_(N,2) to optical mux 62A, wavelength λ_(N,3) tooptical mux 62B, wavelength λ_(N,4) to optical mux 62C, . . . andwavelength λ_(N,1) to optical mux 62N.

In the example implementation, optical pathways 64 are arranged suchthat the different permutations of input interface/wavelengths aredelivered to optical muxes 62. In other words, each optical demux 60 maybe configured to operate in a similar manner, such as λ₁ being providedto a first port of the demux, λ₂ being provided to a second port of thedemux . . . , and λ_(n) being provided to an N^(th) port of the demux.Optical pathways 64 are arranged to optically deliver a specificpermutation of wavelengths to each optical mux 62 such that anycommunications from any one of optical demuxes 60 can reach any opticalmux 62 and, moreover, each permutation of wavelengths is selected toavoid any interference between the signals, i.e., be non-overlapping.

For example, as shown in FIG. 3A, optical paths 64A provide opticalinterconnects from a first port of optical demux 60A carrying λ_(1,1) tooptical mux 62A, from a second port of optical demux 60A carrying 42 tooptical mux 62B, from a third port of optical demux 60A carrying λ_(1,3)to optical mux 62C, . . . and from an N^(th) port of optical demux 60Acarrying to optical mux 62N. Rather than provide an interconnect in thesame way as optical paths 64A, optical paths 64B are arranged to provideoptical interconnects from a first port of optical demux 60B carryingλ_(2,1) to optical mux 62B, from a second port of optical demux 60Bcarrying λ_(2,2) to optical mux 62C, . . . from an N−1^(st) port ofoptical demux 60B carrying λ_(2,n-1) to optical mux 62N, and from anN^(th) port of optical demux 60B carrying λ_(2,n) to optical mux 62A.Optical paths 64C are arranged in yet another manner so as to provideoptical interconnects from a first port of optical demux 60C carryingλ_(3,1) to optical mux 62C, . . . from an N−2^(nd) port of optical demux60C carrying λ_(3,n-2) to optical mux 62N, from an N−1^(st) port ofoptical demux 60C carrying λ_(3,n-1) to optical mux 62A, and from anN^(th) port of optical demux 60C carrying λ_(3,n) to optical mux 62B.This interconnect pattern continues, in this example, such that opticalpaths 64N are arranged to provide optical interconnects from a firstport of optical demux 60N carrying λ_(N,1) to optical mux 62N, from asecond port of optical demux 60N carrying λ_(N,2) to optical mux 62A,from a third port of optical demux 60N carrying λ_(N,3) to optical mux62B, and from a fourth port of optical demux 60N carrying λ_(N,4) tooptical mux 62C, . . . .

In this way, a different permutation of input opticalinterface/wavelength combination is provided to each optical mux 62 and,moreover, each one of the permutations provided to the respectiveoptical mux is guaranteed to include optical communications havingnon-overlapping wavelengths.

Optical permutor 50 illustrates one example implementation of thetechniques described herein. In other example implementations, eachoptical interface 42 need not receive all N wavelengths from a singleoptical fiber. For example, different subsets of the N wavelengths canbe provided by multiple fibers, which would then be combined (e.g., by amultiplexer) and subsequently permuted as described herein. As oneexample, optical permutor 50 may have 2N optical inputs 52 so as toreceive 2N optical fibers, where a first subset of N optical fiberscarries wavelengths λ₁ . . . λ_(n/2) and a second subset of N opticalfibers carries wavelengths λ_(n/2+1) . . . λ_(n). Light from pairs ofthe optical inputs from the first and second set may be combined to formoptical inputs carrying N wavelengths, which may then be permuted asshown in the example of FIG. 3A.

In the example implementation, optical permutor 50, including opticalinput ports 52, optical demuxes 60, optical pathways 64, optical muxes62 and optical output ports 54 may be implemented as one or moreapplication specific integrated circuit (ASIC), such as a photonicintegrated circuit or an integrated optical circuit. In other words, theoptical functions described herein may be integrated on a single chip,thereby providing an integrated optical permutor that may beincorporated into electronic cards, devices and systems.

FIG. 3B is a block diagram another example implementation of opticalpermutor 50. In the example implementation, optical demuxes 60 areconfigured differently so as to direct different respective permutationsof input interface/wavelengths to optical pathways 64 for transport tooptical muxes 62.

In the example implementation of FIG. 3B, each optical demux 60 includesa series of optical circulators 70 having optical grating elements 72disposed after each of the optical circulators. Optical grating elementsmay be, for example Fiber Bragg Grating (FBG) elements or ArrayedWaveguide Grating (AWG). Each pair of optical circulators 70 and Opticalgrating elements 72 is configured to selectively direct a particularwavelength out the corresponding output port of the optical demux 60.Specifically, each optical circulator 70 operates to direct all incominglight received on any of its optical interfaces out a next opticalinterface in a clockwise direction around the circulator. For example,optical circulator 70A receives light on optical interface 74A anddirects all wavelengths around the optical circulator and out opticalinterface 74B. Each Optical grating element 72 is configured to reflecta particular wavelength which re-enters the upstream circulator fromwhich the light was received. For example, Optical grating element 72Areceives wavelengths λ_(1,1), λ_(1,2), . . . λ_(1,n) from upstreamcirculator 70A and is configured to reflect λ_(1,1) and pass all otherwavelengths λ_(1,2), . . . λ_(1,n). Light having λ_(1,1) reenterscirculator 70A where the light is passed to the next optical interface74C to optical pathways 64. Light having wavelengths λ_(1,2), . . .λ_(1,n) continues downstream where optical circulator 70B and Opticalgrating element 72B are configured to selectively direct light havingwavelength λ_(1,2) out optical interface 74D to optical pathways 64. Inthis way, each Optical grating element 72 is configured to selectivelyredirect the correct wavelength out of the appropriate optical ports ofoptical demuxes 60 such that each of the demuxes outputs a differentpermutation of optical wavelengths that are transported to optical muxes62.

In other examples, optical permutors 32, 40, 50 may make use of starcouplers and waveguide grating routers described in Kaminow, “OpticalIntegrated Circuits: A Personal Perspective,” Journal of LightwaveTechnology, vol. 26, no. 9, May 1,2008, the entire contents of which areincorporated herein by reference.

FIG. 4 is a block diagram illustrating an optical permutor 100 having aplurality of logical permutation planes 1-X. Each permutation plane maybe configured substantially as described above so as to permutewavelength/input port combinations to output ports in a manner thatguarantees no interference. Each permutation plane 1-X may, for example,be implemented as optical permutor 40 from FIGS. 2A-2B or opticalpermutor 50 from FIGS. 3A-3B, and the multiple permutation planes may bepackaged on a single chip. In this example implementation, opticalpermutor 100 may readily be scaled in a single device to support highnumbers of optical inputs and outputs.

FIG. 5 is a block diagram illustrating a more detailed exampleimplementation of a network 200 in which a set of access nodes 206 andoptical permutors 204 are utilized to interconnect endpoints in a fullmesh network in which each access node 206 is logically connected toeach of M groups of core switches 209. As shown in this example, eachserver 215 communicates data to any other server via a set of paralleldata paths, as described herein. Network 200 may be located within adata center that provides an operating environment for applications andservices for customers coupled to the data center, e.g., by acontent/service provider network (not shown), such as content/serviceprovider network 7 of FIG. 1. In some examples, a content/serviceprovider network that couples customers to the data center may becoupled to one or more networks administered by other providers, and maythus form part of a large-scale public network infrastructure, e.g., theInternet.

In this example, network 200 represents a multi-tier network having Mgroups of Z physical network core switches 202A-1-202M-Z (collectively,“switches 202”) that are optically interconnected to O optical permutors204-1-204-O (collectively, “OPs 204”), which in turn interconnectendpoints (e.g., servers 215) via Y groups of X access nodes206A-1-206Y-X (collectively, “ANs 206”). Endpoints (e.g., servers 215)may include storage systems, application servers, compute servers, andnetwork appliances such as firewalls and or gateways.

In the example of FIG. 5, network 200 includes three tiers: a switchingtier 210 including switches 202, a permutation tier 212 including OPs204, and an access tier 214A-214Y (herein, “access tier 214”) includingaccess nodes 206. Switching tier 210 represents a set of switches 202,such as core switches 22 of FIG. 1, and typically includes one or morehigh-speed core Ethernet switches interconnected in a switching topologyto provide layer 2 packet switching for packets received on opticallinks from optical permutors 204 and forwarded by the switch fabric onoptical links to optical permutors 204. Switching tier 210 mayalternatively be referred to as a core switch tier/layer or a spineswitch tier/layer.

Each optical permutor from OPs 204 receives light at a set ofwavelengths from each of a set of multiple optical fibers coupled to theoptical permutor and redistributes and outputs the wavelengths amongeach of another set of multiple optical fibers optically coupled to theoptical permutor. Each optical permutor 204 may simultaneously inputwavelengths from access nodes 206 for output to switches 202 and inputwavelengths from switches 202 for output to access nodes 206.

In the example of FIG. 5, network 200 includes Z*M switches 202, Ooptical permutors 204, and Y*X access nodes 206. Access nodes 206 mayrepresent examples of any host network accelerators (HNAs) or othersimilar interface devices, card or virtual device (e.g., router) forinterfacing to optical permutors as described in this disclosure.Optical permutors 204 may represent examples of any optical permutordescribed in this disclosure.

Network 200 may interconnect endpoints using one or more switchingarchitectures, such as multi-tier multi-chassis link aggregation group(MC-LAG), virtual overlays, and IP fabric architectures. Each ofswitches 202 may represent a layer 2 (e.g., Ethernet) switch thatparticipates in the one or more switching architectures configured fornetwork 200 to provide point-to-point connectivity between pairs ofaccess nodes 206. In the case of an IP fabric, each of switches 202 andaccess nodes 206 may execute a layer 3 protocol (e.g., BGP and/or OSPF)to exchange routes for subnets behind each of the access nodes 206.

In the example of FIG. 5, switches 202 are arranged into M groups209A-209M (collectively, “groups 209”) of Z switches. Each of groups 209has a set of switches 202 that are each optically coupled to a sameoptical permutor 204 via a respective optical fiber. Put another way,each of optical permutors 204 is optically coupled to switches 202 ofone of groups 209. For example, group 209A includes switches202A-1-202A-Z optically coupled to respective optical ports of opticalpermutor 204-1. As another example, group 209B includes switches202B-1-202B-Z optically coupled to respective ports of optical permutor204-2.

Each of access nodes 206 includes at least one optical interface tocouple to a port of one of optical permutors 204. For example, accessnode 206A-1 is optically coupled to a port of optical permutor 204-1. Asanother example, access node 206A-2 is optically coupled to a port ofoptical permutor 204-2. In the example of FIG. 5, access nodes 206 aregrouped into Y groups 211A-211Y (collectively, “groups 211”) of X accessnodes. Each of groups 211 has at least one access node 206 opticallycoupled to each of the O optical permutors 204. For example, group 211Ahas access node 206A-1 optically coupled to optical permutor 204-1,access node 206A-2 optically coupled to optical permutor 204-2, and soon through access node 206A-X optically coupled to optical permutor204-O. As a consequence of this topology, each of groups 211 of accessnodes for servers 215 has at least one optical coupling to each ofoptical permutors 204 and, by extension due to operation of opticalpermutors 204, has at least one optical coupling to each of switches202.

In the example of FIG. 5, groups 211 of access nodes 206 includerespective full meshes 220A-220Y of connections to connect access nodes206 of each group pair-wise (point-to-point). Group 211A of access nodes206A-1-206A-X, for instance, includes full mesh 220A of [X*(X−1)]/2point-to-point connections so as to provide full connectivity betweenservers 215 and access nodes 206 for a given group of access nodes towhich the servers connect. Put another way, with full mesh 220A, eachaccess node in group 211A includes at least one point-to-pointconnection to source switching components and destination switchingcomponents in every other access node in group 211A, thereby allowingcommunications to or from switching tier 210 to fan-out/fan-in throughthe access nodes so as to originate from or be delivered to any of theservers 215 via a set of parallel data paths. Connections of full mesh220A may represent Ethernet connections, optical connections or thelike.

Full mesh 220A of group 211A enables each pair of access nodes206A-1-206A-X (“access nodes 206A”) to communicate directly with oneanother. Each of access nodes 206A may therefore reach each of opticalpermutors 204 either directly (via a direct optical coupling, e.g.,access node 206A-1 with optical permutor 204-1) or indirectly viaanother of access nodes 206A. For instance, access node 206A-1 may reachoptical permutor 204-O (and, by extension due to operation of opticalpermutor 204-O, switches 202M-1-202M-Z) via access node 206A-X. Accessnode 206A-1 may reach other optical permutors 204 via other access nodes206A. Each of access nodes 206A therefore has point-to-pointconnectivity with each of switch groups 209. Access nodes 206 of groups211B-211Y have similar topologies to access nodes 206A of group 211A. Asa result of the techniques of this disclosure, therefore, each of accessnodes 206 has point-to-point connectivity with each of switch groups209.

The wavelength permutation performed by each of optical permutors 204 ofpermutation layer 212 may reduce a number of electrical switchingoperations required to perform layer 2 forwarding or layer 2/layer 3forwarding of packets among pairs of access nodes 206. For example,access node 206A-1 may receive outbound packet data from alocally-coupled server 215 and that is destined for an endpointassociated with access node 206Y-1. Access node 206A-1 may select aparticular transport wavelength on which to transmit the data on theoptical link coupled to optical permutor 204-1, where the selectedtransport wavelength is permuted by optical permutor 204-1 as describedherein for output on a particular optical link coupled to a switch ofswitching tier 210, where the switch is further coupled by anotheroptical link to optical permutor 204-O. As a result, the switch mayconvert the optical signal of the selected transport wavelength carryingthe data to an electrical signal and layer 2 or layer 2/layer 3 forwardthe data to the optical interface for optical permutor 204-O, whichconverts the electrical signal for the data to an optical signal for atransport wavelength that is permuted by optical permutor 204-O toaccess node 206Y-1. In this way, access node 206A-1 may transmit data toany other access node, such as access node 206Y-1, via network 200 withas few as a single intermediate electrical switching operation byswitching tier 210.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A network system comprising: a plurality ofservers; a switch fabric comprising a plurality of core switches; aplurality of access nodes, each of the access nodes coupled to a subsetof the servers to communicate data packets with the servers; and aplurality of optical permutation devices optically coupling the accessnodes to the core switches by optical links to communicate the datapackets between the access nodes and the core switches as opticalsignals, wherein each the optical permutation devices comprises a set ofinput optical ports and a set of output optical ports to direct opticalsignal between the access nodes and the core switches to communicate thedata packets, and wherein each of the optical permutation devices isconfigured such that optical communications received from the inputoptical ports are permuted across the output optical ports based onwavelength so as to provide full-mesh optical connectivity between theinput optical ports and the output optical ports without opticalinterference.
 2. The network system of claim 1, wherein the accessnodes, the core switches, and the optical permutation devices areconfigured to provide full mesh connectivity between any pairwisecombination of the servers.
 3. The network system of claim 1, whereinthe access nodes, the core switches, and the optical permutation devicesare configured to connect any pairwise combination of the access nodesby at most a single layer three (L3) hop.
 4. The network system of claim1, wherein the access nodes, the core switches, and the opticalpermutation devices are configured to provide a plurality of paralleldata paths between each pairwise combination of the access nodes.
 5. Thenetwork system of claim 4, wherein, when communicating a packet flow ofpackets between a source server and a destination server, a first one ofthe access nodes coupled to the source server sprays the packets of thepacket flow across the plurality of parallel data paths to a second oneof the access nodes coupled to the destination server, and wherein thesecond one of the access nodes reorders the packets into an originalsequence of the packet flow and delivers the reordered packets to thedestination server.
 6. The network system of claim 5, wherein the firstone of the access nodes coupled to the source server sprays the packetsof the packet flow across the plurality of parallel data paths bydirecting each of the packets to a randomly or round-robin selected oneof the parallel data paths.
 7. The network system of claim 5, whereinthe first one of the access nodes coupled to the source server spraysthe packets of the packet flow across the plurality of parallel datapaths by directing each of the packets to one of the parallel data pathsselected based on available bandwidth of the one of the parallel datapaths.
 8. The network system of claim 1, wherein the core switches arearranged as switch groups and the access nodes are arranged as accessnode groups, wherein each of the optical permutation devices isoptically coupled one or more access nodes in each of the access nodegroups, and wherein each of the optical permutation devices is opticallycoupled to the core switches of a different respective one of the switchgroups.
 9. The network system of claim 1, wherein each of the opticalpermutation devices comprises: a plurality of the input optical ports toreceive respective optical signals, wherein the respective opticalsignals comprise optical communications at a plurality of differentwavelengths; a plurality of the output optical ports to output opticalsignals; and a set of optical elements arranged to provide opticalinterconnection between the optical input ports and the optical outputports, wherein the set of optical elements are configured to direct arespective unique and non-interfering permutation of the wavelengthsfrom the input optical ports to the output optical ports.
 10. Thenetwork system of claim 9, wherein the plurality of differentwavelengths within each of the optical communications comprises Nwavelengths; and wherein the set of optical elements comprises a set ofoptical multiplexors/demultiplexors each configured to receive adifferent subset of the optical signals from the input ports andoptically direct the N wavelengths from each of the optical signals ofthe different subset across N of the output ports to direct therespective unique and non-interfering permutation of the N wavelengthson each of the output optical ports.
 11. The network system of claim 10,wherein each of the optical permutation devices comprises: a pluralityof optical multiplexor/demultiplexor slices each configured to receivethe optical signals from a different subset of the input ports and tooptically direct the wavelengths from each of the optical signals of thedifferent subset across the output ports to direct the unique andnon-interfering permutations of the wavelengths on each of the outputoptical ports.
 12. The network system of claim 11, wherein each of theoptical multiplexor/demultiplexor slices comprises a plurality ofoptical mux/demux chips, wherein the different subset of the input portscomprises four input ports, and wherein the N wavelengths from each ofthe optical signals comprise four unique wavelengths, and wherein eachof the optical mux/demux chips of each of the opticalmultiplexor/demultiplexor slices is configured to: receive an opticalsignal from each of the four input ports coupled to the respectiveoptical multiplexor/demultiplexor slice, split the four wavelengths ineach of the optical signals, and spray the four wavelengths carried byeach of the optical signals such that the optical output ports eachcarry a different one of the possible unique permutations of thecombinations of the four input ports and the four wavelengths carried bythose four input ports and where no single optical output port carriesmultiple optical communications having the same wavelength.
 13. Thenetwork system of claim 12, wherein each of the optical permutationdevices comprises: sixteen input optical ports to receive the opticalsignals from the servers, sixteen output optical ports to output theoptical signals to the core switches, and four opticalmultiplexor/demultiplexor slices, each comprising at least one opticalmux/demux chip.
 14. The network system of claim 1, wherein each of theaccess nodes comprises: a source component operable to receive trafficfrom a server; a source switching component operable to switch sourcetraffic to other source switching components of different access nodesor toward the core switches via the optical permutation devices, adestination switching component operable to switch inbound trafficreceived from other source switching components or from the coresswitches via the optical permutation devices; and a destinationcomponent operable to reorder packet flows received via the destinationswitching component and provide the packet flows to a destination servercoupled to the access node.
 15. The network system of claim 1, whereinthe access nodes, the core switches, and the optical permutation devicesare configured to provide full mesh connectivity between any pairwisecombination of the servers, and wherein the full-mesh interconnectivityof the switch fabric between the servers is non-blocking and drop-free.16. The network system of claim 1, wherein one or more of the accessnodes comprise storage devices configured to provide network accessiblestorage for use by applications executing on the servers.
 17. A methodcomprising: interconnecting a plurality of servers of a data center byan intermediate network comprising: a switch fabric comprising aplurality of core switches; a plurality of access nodes, each of theaccess nodes coupled to a subset of the servers to communicate datapackets with the servers; and a plurality of optical permutation devicesoptically coupling the access nodes to the core switches by opticallinks to communicate the data packets between the access nodes and thecore switches as optical signals, wherein each of the opticalpermutation device comprise a set of input optical ports and a set ofoutput optical ports to direct optical signal between the access nodesand the core switches to communicate the data packets, wherein each ofthe optical permutation devices is configured such that opticalcommunications received from the input optical ports are permuted acrossthe output optical ports based on wavelength to provide full-meshoptical connectivity between the input optical ports and the outputoptical ports without optical interference, and wherein the accessnodes, the core switches, and the optical permutation devices areconfigured to provide a plurality of parallel data paths between eachpairwise combination of the access nodes; and communicating a packetflow between the servers including spraying, with the access nodes,packets of the packet flow across the plurality of parallel data pathsbetween the access nodes, and reordering, with the access nodes, thepackets into the packet flow and delivering the reordered packets. 18.The method of claim 17, wherein the access nodes, the core switches, andthe optical permutation devices are configured to provide full meshconnectivity between any pairwise combination of the servers.
 19. Themethod of claim 17, wherein the access nodes, the core switches, and theoptical permutation devices are configured to connect any pairwisecombinations of the access nodes by at most a single layer three (L3)hop.
 20. A method for forwarding communications within a packet-basednetwork, the method comprising: receiving packet-based communicationswith a set of optical input ports of an optical permutation device,wherein the set of optical input ports couple the optical permutationdevice to a set of access nodes positioned between the opticalpermutation device and a set of servers with a packet-based network;permuting the packet-based communications across a set of output opticalports of the optical permutor based on wavelength to provide full-meshoptical connectivity between the input optical ports and the outputoptical ports of the optical permutor without optical interference; andforwarding, with the optical permutor and by the set of output ports,the permuted packet-based communications toward a set of one or moreswitches within the networks.
 21. An optical permutation devicecomprising: a plurality of the input optical ports to receive respectiveoptical signals, wherein the respective optical signals comprise opticalcommunications at a plurality of different wavelengths; a plurality ofthe output optical ports to output optical signals; and a set of opticalelements arranged to provide optical interconnection between the opticalinput ports and the optical output ports, wherein the set of opticalelements are configured to direct a respective unique andnon-interfering permutation of the wavelengths from the input opticalports to the output optical ports.
 22. The optical permutation device ofclaim 21, wherein the plurality of different wavelengths within each ofthe optical communications comprises N wavelengths; and wherein the setof optical elements within the optical permutor comprises a set ofoptical multiplexors/demultiplexors each configured to receive adifferent subset of the optical signals from the input ports andoptically direct the N wavelengths from each of the optical signals ofthe different subset across N of the output ports to direct therespective unique and non-interfering permutation of the N wavelengthson each of the output optical ports.
 23. The optical permutation deviceof claim 21, further comprising a plurality of opticalmultiplexor/demultiplexor slices each configured to receive the opticalsignals from a different subset of the input ports and to opticallydirect the wavelengths from each of the optical signals of the differentsubset across the output ports to direct the unique and non-interferingpermutations of the wavelengths on each of the output optical ports. 24.The optical permutation device of claim 23, wherein each of the opticalmultiplexor/demultiplexor slices comprises a plurality of opticalmux/demux chips, wherein the different subset of the input portscomprises four input ports, and wherein the N wavelengths from each ofthe optical signals comprise four unique wavelengths, and wherein eachof the optical mux/demux chips of each of the opticalmultiplexor/demultiplexor slices is configured to: receive an opticalsignal from each of the four input ports coupled to the respectiveoptical multiplexor/demultiplexor slice, split the four wavelengths ineach of the optical signals, and spray the four wavelengths carried byeach of the optical signals such that the optical output ports eachcarry a different one of the possible unique permutations of thecombinations of the four input ports and the four wavelengths carried bythose four input ports and where no single optical output port carriesmultiple optical communications having the same wavelength.
 25. Theoptical permutation device of claim 24, wherein each of the opticalpermutation devices comprises: sixteen input optical ports to receivethe optical signals from the servers, sixteen output optical ports tooutput the optical signals to the core switches, and four opticalmultiplexor/demultiplexor slices, each comprising at least one opticalmux/demux chip.
 26. The optical permutation device of claim 21, whereinthe optical permutation device comprises a photonic integrated circuit.